Simplify the following expression: $y = \dfrac{-9k}{3} - \dfrac{9k}{3}$
Since the expressions have the same denominator we simply combine the numerators: $y = \dfrac{-9k - (9k)}{3}$ Combine like terms: $y = \dfrac{-18k}{3}$ Simplify by dividing numerator and denominator by 3: $y = \dfrac{-6k}{1}$ $y = -6k$